Novel symptomatology and changing epidemiology of domoic acid toxicosis in California sea lions (Zalophus californianus): an increasing risk to marine mammal health.

Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.

Cell cycle regulation in a dinoflagellate, Amphidinium operculatum: identification of the diel entraining cue and a possible role for cyclic AMP.

This research describes the diel phasing of the cell cycle in the dinoflagellate, Amphidinium operculatum Claparéde and Lachmann, and investigates the mechanisms that serve to link the cell cycle to the diel cycle. Unlike many dinoflagellates, A. operculatum has a naturally high division rate of approximately 1 division day(-1), which yields a nearly synchronous population, making it useful for population studies. When grown on a 16:8 h light/dark cycle, S-phase begins 10 h and mitosis 14-16 h after the onset of light, as determined by flow cytometry. Alterations in the timing of the dark/light and light/dark transitions showed that the cell cycle is entrained by the dark/light transition, with the light/dark cue being uninvolved. Cells in logarithmic phase growth also undergo diel changes in cell size (9-14 &mgr;m), reaching a maximum size late in the light phase, concurrent with mitosis. Stationary phase cells or cells blocked in G1 of the cell cycle with a cell cycle inhibitor, olomoucine, showed no size changes or reduced size changes over the diel cycle, suggesting a coupling of cell size to the cell division cycle. In Euglena, cAMP-dependent signaling appears to mediate diel phasing of the cell cycle. Therefore, the role of cAMP in cell cycle control in A. operculatum was investigated. Measurement of intracellular cAMP by radioimmunoassay (RIA) revealed that cAMP concentrations varied on a diel basis, but increases observed appeared to correlate with cell size increases, and did not correlate with light cues at the dark/light or light/dark transition. However, when cells were treated with the cAMP phosphodiesterase inhibitor, IBMX, cell cycle progression was inhibited at both the G1/S and the G2/M phase transitions. This supports a role for cAMP-dependent signaling in the dinoflagellate cell cycle and is in agreement with the documented role of cAMP in the cell cycle control of higher eukaryotes.